1. Field of the Invention
The present invention relates to an ink jet recording apparatus equipped with a recovery mechanism for maintaining and recovering satisfactory ink discharge state.
2. Related Background Art
The ink jet recording apparatus achieves printing on paper by discharging liquid ink from a head. As shown in FIG. 25, a carriage 101, supporting a printing head 105 and an ink tank or an ink supply tube, moves in a print-scanning direction to effect printing on the paper.
The conventional ink jet recording apparatus is usually equipped with a cap for tightly covering the nozzle-bearing face of the printing head when the printing operation is not effected, in order to prevent drying of the printing head and leakage of printing ink from the head. Also an ink-sucking pump is usually provided in communication with the cap, for recovering from printing defect resulting from the nozzle clogging with dusts or from air entrusion into the nozzle.
Recently there is becoming popular the apparatus utilizing plural printing heads and inks of plural colors for enabling color printing. There are at least required three colors of cyan, magenta and yellow for full color printing, and the main trend is in the printers utilizing inks of four colors, including black in addition to the above-mentioned three colors. As a result there are provided plural caps for respective printing heads, and the color printer is equipped with four caps.
FIG. 25 is a schematic view of an ink jet recording apparatus, wherein provided are a carriage 101; a main body 102 including a paper transporting unit; a recovery mechanism 103 for the recovery operation for the printing head; and printing heads 105. The carriage 101 is rendered movable along a guide shaft 111, and is driven by a carriage motor 115 through a belt 114. When the main body receives printing data, the carriage 101 effects scanning motion along the guide shaft 111, in order to effect printing on a sheet of paper, to be transported by an unrepresented paper transporting unit. In the vicinity of the carriage there is provided an encoder film 113 for detecting the absolute position of the carriage, and an encoder mounted on the carriage detects the absolute position of the carriage. The home position of the carriage is thus determined.
FIG. 26 is a perspective view of an example of the conventional recovery mechanism, wherein shown are a cap 131; a cap holder 132 supporting the cap; a pump 135; and a lever 136 for activating the pump. FIG. 27 is a cross-sectional view seen in a direction indicated by arrows A' in FIG. 26, wherein illustrated are a cam gear 137 for actuating the lever; and a motor 139 for actuating the cam gear 137. When the printing operation is terminated, the carriage 101 stops in facing relationship to the recovery mechanism, at the home position of the above-mentioned encoder film 113. In this state the recovery motor 139 is activated in the forward direction to rotate the cam gear 137 through a worm gear, whereby the cap holder 132 ascends along a cam groove formed on the lateral face of the cam gear and the cap 131, movably supported by the cap holder, is brought into tight contact with the head 105. Such capping operation prevents the drying of the printing head, thereby maintaining the performance thereof when the printing operation is not in progress. Also reverse rotation of the recovery motor 139 rotates the cam gear 137 to actuate a piston 151 of the pump 135 through the lever 136, thereby generating a negative pressure in the pump. Said negative pressure is transmitted to the interior of the cap, through a suction tube 134 connecting the pump 135 with the cap, thereby sucking ink from the nozzles of the printing head maintained in contact with the cap and thus recovering the printing performance of the printing head.
As explained in the foregoing, the conventional ink jet recording apparatus is equipped with a discharge recovery device for eliminating causes of defective ink discharge, such as the nozzle blocking by ink drying, dusts and bubbles in the ink. Such recovery device principally performs following two functions.
The first function is the ink suction removal, by covering the nozzle-bearing face, containing the nozzles, with the cap made of an elastic material such as rubber and sucking the air inside the cap with the pump or the like, thereby forcedly discharging the ink from the nozzles and thus eliminating the above-mentioned causes.
The second function is the removal of unnecessary ink deposited on the above-mentioned nozzle-bearing face, thus rendering the direction of discharge of ink droplets unstable and deteriorating the print quality. This function is achieved by a wiper blade composed of an elastic member and capable of wiping said nozzle-bearing face or an absorbent member, composed for example of a porous material, and brought into contact with said nozzle-bearing face when required, thereby absorbing and removing said unnecessary ink.
However, when the above-mentioned ink suction removal is executed on the recording head, there results a phenomenon of reverse flow of the ink, remaining in the cap, into the nozzles of the recording head by the ink flow within the cap. For this reason, if there is provided only one discharge recovery device in a recording apparatus capable of discharging plural inks (for example a color ink jet recording apparatus), there may result a drawback of defective print quality because of mixing of different inks.
Such inconvenience may be avoided by sucking a large amount of ink or discharging ink after such sucking, in order to completely eliminate such reverse flowing ink within the step of ink suction removal, but such method leads to an elevated running cost because the ink amount discharged other than the recording purpose increases. Also the used ink tank, for storing thus discharged ink within the recording apparatus, has to be made larger, so that the entire recording apparatus inevitably becomes larger.
Also if the discharge recovery devices are provided respectively corresponding to the inks of different kinds, there results an increased cost due to the increase in number of the component parts, in addition to the increase in dimension of the entire recording apparatus.
In the conventional apparatus, as explained above, four caps are respectively provided with pumps, and, at the ink sucking operation, such four pumps are either simultaneously or independently activated. The former method is associated with drawbacks of wasted ink consumption because the ink suction is executed even on the recording head not requiring such ink suction and of necessity for a larger motor because of the large load, while the latter method is associated with a drawback of requiring a complex driving mechanism for independent activation of the pumps.
As explained in the foregoing, in an ink jet recording apparatus capable of recording with plural inks, the discharge recovery device free from color mixing is contradictory to the compactization of the entire recording apparatus, so that it has been impossible to compactize the ink jet recording apparatus, for example capable of color printing, into a size suitable for use in a notebook-sized personal computer.
Also in the recording apparatus equipped with plural recording heads, the discharge recovery device may be compactized, as disclosed in the U.S. Pat. Nos. 4,492,969, 4,506,277 and 4,510,510, by providing plural caps respectively corresponding to the inks of different kinds and connecting all these caps to a single pump. However, if the level of ink adhesion, resulting for example from ink drying, is different among the plural recording heads, the ink is not sucked from the recording heads with severe ink adhesion but only from those with little ink adhesion, so that the recovery of ink discharge cannot be achieved satisfactorily.
Besides, even if the above-mentioned drawback can be avoided for example by applying a sufficiently large instantaneous suction pressure to the caps, this method effects the recovery of ink discharge also on the recording heads which do not require such recovery, thereby causing unnecessary large ink consumption and thus elevating the running cost.